Coal is a major source of energy in the United States and is increasing in importance because of the abundance within the United States and because of the security and balance of payments problems which arise from our reliance on foreign oil. A very promising process is the gasification of coal to produce gas for pollution free combustion and as a petrochemical feedstock but this requires the need to pump large quantities of coal into the reactor.
Transport problems constitute one of the major difficulties in the use of coal. Aqueous slurries of finely ground coal containing more than about 55 weight percent solids are difficult to transport using conventional slurry pumps because as the solids level is increased above about 50 weight percent the water and solids tend to separate causing coal particles to build up in various areas throughout the pumping system. This dewatering of the slurry causes blockage and jamming of the pumping system. For similar reasons coal slurries containing above about 65 weight percent solids have not heretofore been capable of being extruded continuously using an extruder.
It is desirable to decrease the weight percent of water in aqueous coal slurries because water is a major contributor to the cost of transport and processing operations. The less water transported the greater is the volume of coal that can be moved, resulting in transport efficiencies. Also during coal gasification a significant amount of heat is required to vaporize the water vehicle. As the weight percent of the water vehicle decreases, the efficiency of the coal gasification process increases. A method which allows the use of higher weight percent solids aqueous coal slurries than were heretofore feasible would be of great importance.